[Bug 278930] x11/xorg no support of DisplayPort 1.2 specification, resulting a blank screen till reboot

From: <bugzilla-noreply_at_freebsd.org>
Date: Mon, 13 May 2024 17:52:20 UTC
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=278930

--- Comment #2 from Rostislav Krasny <rosti.bsd@gmail.com> ---
Hi Marcin and thank you for your quick response.

After further investigation it turned out that the problem is not related to
the DisplayPort 1.2 mode at all and I was just got confused by circumstances.
Let me tell all the story again.

1. I installed FreeBSD 14.1-BETA2.
2. I installed LXQT, sddm, Xorg and video drivers. Then I tried to log into the
LXQT session and ran into the blank screen problem for the first time.
3. Without removing LXQT and sddm (but I disabled sddm in the /etc/rc.conf) I
installed XFCE and lightdm. When I tried the XFCE I ran into the blank screen
problem second time and though this is some global issue.

4. I decided to try something different and installed the latest snapshot of
DragonFlyBSD with Xorg and some dm instead of the previously installed FreeBSD.
DragonFlyBSD has the blank screen problem as well, even in the dm login page.
This was the first time when I opened my internal monitor settings and disabled
the DisplayPort 1.2 support. This fixed the problem in the DragonFlayBSD and I
decided to go back to the FreeBSD 14.1-BETA2. That "fix" confused me and this
is why I thought the problem in FreeBSD is the same.

5. I installed FreeBSD 14.1-BETA2 again.
6. Installed Xorg, video drivers, XFCE and lightdm but not LXQT and video works
fine even with DisplayPort 1.2 enabled.

Installing LXQT even without sddm brings this problem back. Running "pkg delete
lxqt && pkg autoremove" fixes it. So this is something in LXQT and it brakes
all other installed DEs.

I will change the title of this bug report.

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